app/django/contrib/gis/db/backend/postgis/field.py
author Sverre Rabbelier <sverre@rabbelier.nl>
Mon, 07 Sep 2009 20:27:37 +0200
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from django.db import connection
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from django.db.models.fields import Field # Django base Field class
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from django.contrib.gis.db.backend.util import gqn
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from django.contrib.gis.db.backend.postgis.query import TRANSFORM
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# Quotename & geographic quotename, respectively
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qn = connection.ops.quote_name
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class PostGISField(Field):
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    """
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    The backend-specific geographic field for PostGIS.
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    """
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    def _add_geom(self, style, db_table):
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        """
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        Constructs the addition of the geometry to the table using the
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        AddGeometryColumn(...) PostGIS (and OGC standard) stored procedure.
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        Takes the style object (provides syntax highlighting) and the
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        database table as parameters.
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        """
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        sql = style.SQL_KEYWORD('SELECT ') + \
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              style.SQL_TABLE('AddGeometryColumn') + '(' + \
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              style.SQL_TABLE(gqn(db_table)) + ', ' + \
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              style.SQL_FIELD(gqn(self.column)) + ', ' + \
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              style.SQL_FIELD(str(self._srid)) + ', ' + \
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              style.SQL_COLTYPE(gqn(self._geom)) + ', ' + \
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              style.SQL_KEYWORD(str(self._dim)) + ');'
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        if not self.null:
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            # Add a NOT NULL constraint to the field
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            sql += '\n' + \
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                   style.SQL_KEYWORD('ALTER TABLE ') + \
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                   style.SQL_TABLE(qn(db_table)) + \
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                   style.SQL_KEYWORD(' ALTER ') + \
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                   style.SQL_FIELD(qn(self.column)) + \
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                   style.SQL_KEYWORD(' SET NOT NULL') + ';'
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        return sql
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    def _geom_index(self, style, db_table,
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                    index_type='GIST', index_opts='GIST_GEOMETRY_OPS'):
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        "Creates a GiST index for this geometry field."
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        sql = style.SQL_KEYWORD('CREATE INDEX ') + \
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              style.SQL_TABLE(qn('%s_%s_id' % (db_table, self.column))) + \
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              style.SQL_KEYWORD(' ON ') + \
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              style.SQL_TABLE(qn(db_table)) + \
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              style.SQL_KEYWORD(' USING ') + \
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              style.SQL_COLTYPE(index_type) + ' ( ' + \
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              style.SQL_FIELD(qn(self.column)) + ' ' + \
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              style.SQL_KEYWORD(index_opts) + ' );'
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        return sql
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    def post_create_sql(self, style, db_table):
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        """
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        Returns SQL that will be executed after the model has been
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        created. Geometry columns must be added after creation with the
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        PostGIS AddGeometryColumn() function.
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        """
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        # Getting the AddGeometryColumn() SQL necessary to create a PostGIS
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        # geometry field.
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        post_sql = self._add_geom(style, db_table)
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        # If the user wants to index this data, then get the indexing SQL as well.
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        if self._index:
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            return (post_sql, self._geom_index(style, db_table))
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        else:
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            return (post_sql,)
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    def _post_delete_sql(self, style, db_table):
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        "Drops the geometry column."
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        sql = style.SQL_KEYWORD('SELECT ') + \
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            style.SQL_KEYWORD('DropGeometryColumn') + '(' + \
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            style.SQL_TABLE(gqn(db_table)) + ', ' + \
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            style.SQL_FIELD(gqn(self.column)) +  ');'
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        return sql
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    def db_type(self):
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        """
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        PostGIS geometry columns are added by stored procedures, should be
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        None.
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        """
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        return None
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    def get_placeholder(self, value):
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        """
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        Provides a proper substitution value for Geometries that are not in the
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        SRID of the field.  Specifically, this routine will substitute in the
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        ST_Transform() function call.
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        """
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        if value is None or value.srid == self._srid:
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            return '%s'
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        else:
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            # Adding Transform() to the SQL placeholder.
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            return '%s(%%s, %s)' % (TRANSFORM, self._srid)